Add LFS check

If somebody clones the repo without Git LFS installed then they won't see any errors but will have 'corrupted' VGF/npy files which lead to confusing error messages when running the scenario. This patch adds a line to the cloning instructions to check that LFS has been configured correctly, to catch this issue earlier.

README.md

@@ -77,6 +77,7 @@ Clone the NSS model repository from Hugging Face
 ```powershell
 git clone https://huggingface.co/Arm/neural-super-sampling
 cd neural-super-sampling
+git lfs pull # Make sure Git LFS is installed - https://git-lfs.com/
 ```
 
 ### Run the Scenario